Now, why in the world would you consider parking in a handicap spot (just because you're entitled to use it, for its intended purpose) when you know you'll be inconveniencing some poor soul who wants to use it so they don't have to walk as far when they're unloading their groceries? I'm sure that person has more right to use it than you do...after all, I'll bet they've done everything right, voted for Obama, held their hand out for anything they could get, (aw, hell, I could go on and on!) and yet you insist on using that spot instead!
(Heavy sarcasm there...

)
I'd put up a sign, as big as I could find, and say something like -
To the individual who left the note on my vehicle: My apologies for being, as you put it, "Rude and Inconsiderate". I feel bad that my disability is inconveniencing others "who need to use the space". You probably just got your welfare check and food stamps, and had a lot of groceries paid for by other's tax dollars that you needed to carry in, and my inconsideration in using a handicap space for what it is intended for was inexcusable. Since you left no name or phone number on your note, I'll assume that you have no more balls than a mouse, and would probably wet yourself if there was an actual confrontation on this subject. So how about you just go f*** yourself, and leave me alone?